This invention relates to large dynamoelectric machines of the type used in power plants; and, in particular, this invention relates to terminal boxes which are included as part of the dynamoelectric machine structure.
The terminal box of a large dynamoelectric machine provides a housing for the high voltage bushings which conduct electrical current out of the dynamoelectric machine. Stray magnetic flux from the phase leads and neutral leads, as they are carried through the terminal box by the high voltage bushings, will impinge upon the walls of the terminal box and cause circulating currents. This can lead to heating of the terminal box walls in some locations depending upon the orientation of the walls and their location with respect to the bushings.
The use of flux shields in various portions of a dynamoelectric machine is well known. These generally consist of sheets of conductive material placed between the source of stray flux and the member which is to be shielded. Circulating currents are set up in the flux shield itself which then tend to repel stray flux from entering the shielded member. Large dynamoelectric machines are typically cooled by hydrogen gas and further this gas cooling may be extended to the terminal box vis-a-vis the physical connection of the terminal box to the dynamoelectric machine. Moreover, the terminal bushings may be directly or indirectly cooled by means of the hydrogen gas (U.S. Pat. No. 2,742,582; Bahn et al). In U.S. Pat. No. 4,029,978 to Jager et al, liquid cooling of the terminal bushings is demonstrated.
In U.S. Pat. No. 3,808,489 to Albright et al, the terminal box for the high voltage bushings of a dynamoelectric machine is provided with special flux shields to reduce heating of the terminal box walls caused by circulating currents due to stray flux from the high voltage bushings. The flux shield and terminal box walls are then cooled by gas flowing through special passages between them. The shield is spaced from the walls and means are provided for inducing a flow of cooling gas to cool both the walls and the flux shield. The shield is arranged to create the greatest cooling at the location where heating is most likely to occur.
Finally, U.S. Pat. No. 3,435,262 to Bennett et al discloses core end flux shields for use in a dynamoelectric machine wherein the core end flux shields are liquid cooled.